Hermetically-sealed, motor compressor unit including noise reducing means



March 15, 1960 P. E. DAVEY 2,928,589

HERMETICALLY-SEALED, MOTOR COMPRESSOR UNIT mcwnmc NOISE REDUCING MEANSFiled 001;. 31, 1958 A INVENTOR. F i G PETER E. DAVEY H15 ATTORNEYUnited States Patent HERMETICALLY-SEALED, MOTOR COMPRESSOR UNITINCLUDING NOISE REDUCING MEANS leter E. Davey, Fern Creek, Ky., assignorto General Electric Company, a New York corporation Application October31, 1958, Serial No. 771,089 3 Claims. (Cl. 230-232) The presentinvention relates to hermetically sealed motor-compressor units and ismore particularly concerned with a simple and inexpensive arrangementfor reducing the noise energy. emanating from such a unit.

itiermetically'sealed motor-compressor units such as those used in therefrigerationindustry comprise a compressor and a motor for driving thecompressorv suitably supported within a hermetically sealed casing. Thecasing is filled with either high or low pressure refrigerant beingcirculated through a refrigerating system by the compressor and normallythere is a body of lubricating oil disposed in the bottom portion of thecasing for lubricating the compressor. Due to the large variety ofmoving parts in such a unit, the total noise energy emanating from theunit during operation of the compressor comprisesmany differentfrequencies and qualities. The various noise sources, each of which mayhave its own exciting frequency, are not limited to the valve noises ofthe compressor resulting from the rapid opening and closing of thecompressor valves, the mechanical vibrations of the compressor cylinderand mount and supports caused by the reciprocating movement of thepiston and the linkage noises between the piston and the driving motor,but also include the various noises emanating from the motor itself dueto axial movement of the rotor under the magnetic forces acting thereon,the slight changes in the rotational velocity of the rotor due to thechanging load conditions thereon during each compressor cycle, and thevibrations set up as the rotor bars move past the stator slots. All ofthese noises from the motor-compressor unit may be transmitted to thecasing and may produce a high or aggravating noise level outside thecasing. The trans mission may be either through the means for supportingor suspending the motor-compressor unit within the C38, ing or by thegas contained within the casing.

The present invention is particularly concerned with means for reducingthe noises transmitted by or set up in the gas contained within thecompressor casing. These noises, frequently referred to collectively ascavity resonance, include those vibrations set up within the gascontained in the casing due to the rotation of the slotted rotor andthose set up in the gas due to the vibration of other parts of themotor-compressor unit. Broadly, the frequencies and nature of thevibrations involved in cavity resonance in any particular hermeticcompressor will depend upon a number of factors, including the gaspressure in the case, the geometry of the case including its volume andother dimensions and the particular exciting frequencies produced by themotorcompressor unit.

In accordance with the present invention, cavity resonance in ahermetically sealed motor-compressor unit is substantially decreased byproviding within the hermetic casing and between the casing and themotorcompressor unit suspended therein, a curtain in the form of a wovencloth suitably suspended at spaced points from the top of the casing sothat the free portions iice including the lower edges thereof are drapedbetween the compressor and the casing. It is found that such a curtaineffectively breaks up standing waves in thegas within the casing andabsorbs some of their energy so that there is not only an overallreduction in the noise energy but also a significant damping of the puretones or howls frequently produced by high speed compressors, whichtones unless damped have a relatively high and disturbing noise level,The cloth employed in the practice of the present invention is composedof tightly woven fibers of a material which is chemically inert withregards to the refrigerant such as the dichloro difiuoro methanegenerally employed in household refrigerating systems and chemicallyinert with reference to the lubricant employed for lubricating thecompressor. Particularly suited to the practice of the present inventionare the synthetic fibers made from the esterification product ofethylene glycol and terephthalic acid and commercially available underthe trade name Dacron."

For a better understanding of the invention reference may be had to theaccompanying drawing in which:

Fig. 1 is a vertical sectional view of a typical hermetically sealedmotor-compressor unit embodying the present invention; and

Fig. 2 is a side elevational view of the compressor of Fig. 1 partiallyin section along line 22 of Fig. 1.

With reference to the drawing, the disclosed embodiment of the presentinvention includes a hermetically sealed casing 1 containing ahorizontally disposed motorcompressor unit including a motor 2 and acompressor 3 connected by a drive shaft (not shown) to the motor 2. Itwill be understood of course that this type of compressor unit isadapted to withdraw refrigerant from the evaporator compo nent'of arefrigerating system and to discharge compressed refrigerant from thecompressor 3 to the condenser compartment of that system. Either thehigh or the low side of the system will be connected to the case and theother side to the compressor so that the refrigerant flowing between thesystem and the compressor will pass through the case and completely fillthe interior thereof.

In the illustrated embodiment of the invention the motor-compressor unitis suspended within the casing by means of a plurality of tensionsprings 5 having their upperends secured to the casing and their lowerends secured to the motor-compressor unit.

1 For the purpose of lubricating the motor-compressor unit there isprovided a body of oil 6 in the bottom portion of the casing 1 and oilis withdrawn through a tube 8 by means of a suitable pump (not shown)formingpart of the motor-compressor unit for distribution to thebearings and other moving parts of the motorcompressor unit requiringcooling or lubrication or both.

During operation of the compressor the noises generated in the motor 2and the compressor 3 are of various frequencies and energy or soundlevels. Some of these noises are transmitted to the case through thespring suspension and may be damped or partially damped by the properdesign of this suspension. Others are transmitted through or set up inthe refrigerant gas contained within the casing 1. The present inventionis particularly concerned with the damping of these gas borne or gasgenerated noises and to this end there is provided :between themotor-compressor unit and the walls defin- MM, m."

3 a suitable material for this purpose and it is desirable that thecloth be of a fine or closely woven mesh in which adjacent parallelthreads are in contact with one another.

For maximum noise reduction, as much as possible of the curtain 7 shouldbe freely draped in the space between the motor-compressor unit and thecasing and for that purpose the curtain is suspended or secured to thecasing at'a minimum number of points. In the illustrated embodiment ofthe invention it will be seen that the curtain is suspended by means ofone or more fasteners 10 to the outer portion of the top wall 11 of thecasing and draped generally from these fasteners to the spring supports12 provided on the side walls of the compressor casing which areemployed to anchor the curtain 7 in such a manner that its lower or freeends 14 will suspend or hang freely from the supports 12 downwardlybetween the side walls of the casing and the motor-compressor unit.

More specifically, it will be seen that with the curtain 7 fastened onlyto the center top portion of the case by the fasteners 10 and to theside walls of the case by means of the spring supports 12, the portionsof the curtain between these fasteners hangs loosely or drapes betweenthe supports in spaced relationship with both the motorcompressor unitand the compressor case while the free ends 16 of the curtain below thespring supports 12 hang loosely between the sides of themotor-compressor unit and the side walls of the case. Preferably, thelower end of the curtain 7 is above the level of the oil 6 in thecompressor case as it has been found that a dry curtain, that is, acurtain which is not soaked with oil has better noise dampingcharacteristics than one that is. While some oil may be thrown onto thecurtain during operation of the compressor as for example from therevolving counter weight 18 most of this oil will drain from the curtainand with the lower end of the curtain above the oil level there is nowick action to provide a continuous flow of oil by capillary attractionupwardly into the curtain.

' With the curtain 7 supported at the minimum number of points on thecompressor case and otherwise hanging loosely away from both the caseand the motor-compressor unit, there is obtained a substantial reductionin cavity resonance particularly in the range of from about 900 to 3500cycles per second noise energies. The curtain is particularly effectivein damping pure tone noises which are generated in the gas within thecasing 1 and which due to the conditions existing within the case as forexample with particular gas pressures and the case geometry and so forthmay otherwise be amplified to an abnormally high energy level. Thecurtain provides inexpensive damping of case resonance by means of amaterial which is chemically inert both with reference to therefrigerant contained in the case and the oil. It is believed theattenuation of noise by means of the curtain 7 results both from amotion of the curtain or the freely draped portions thereof in the soundfield accompanied also by some small absorption of noise in the smallcapillaries or interstices existing between the Dacron fibers so that itsubstantially prevents cavity resonance by breaking up standing wavesand absorbing some of the energy whereby the pure tone vibrations in thecompressor noise spectrum are eliminated.

While the present invention has been described with reference to aparticular embodiment thereof it will be understood that the inventionis not limited thereto and it is intended by the appended claims tocover all such modifications as come within the spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A hermetic compressor including a sealed casing, a motor-compressorunit resiliently suspended within said casing in spaced relation withthe walls of said casing and means for damping cavity resonancecomprising a cloth curtain disposed between said casing and at least thetop and sides of said motor-compressor unit, said curtain being fastenedto the interior of said casing at a plurality of spaced points with theunsupported portions of said curtain draping in spaced relation withsaid casing and said motor-compressor unit.

2. A hermetic refrigerant compressor including a sealed casingcontaining refrigerant, a motor-compressor unit resiliently suspendedwithin said casing in spaced relation with the walls of said casing andmeans for damp ing cavity resonance comprising a cloth curtain composedof fibers inert with regards to said refrigerant and disposed betweensaid casing and at least the top and sides of said motor-compressorunit, said curtain being fastened to the interior of said casing at aplurality of spaced points with the unsupported portions of said curtaindraping in spaced relation with said casing and said motor-compressorunit.

3. A hermetic compressor including a sealed casing, a motor-compressorunit resiliently suspended within said casing in spaced relation withthe walls of said casing and means for damping cavity resonancecomprising a cloth curtain disposed between said casing and at least thetop and sides of said motor-compressor unit, said curtain being fastenedonly to the top and side walls of said casing at a plurality of spacedpoints with the unsupported portions of said curtain draping in spacedrelation with said casing and said motor-compressor unit.

References Cited in the file of this patent UNITED STATES PATENTS1,660,745 Delaney Feb. 28, 1928 1,730,529 Robbins Oct. 8, 1929 2,072,035Hayenga et a1. Feb. 23, 1937 2,721,029 Grimshaw Oct. 18, 1955 2,741,425Scheldorf Apr. 10, 1956

